FastLineRenderableSeries RolloverMarkerTemplate swap from code behind

I’m trying to switch RolloverMarker template at runtime from code behind, with no luck.
I have ControlTemplate definitions in XAML.
I create FastLineRenderableSeries objects and assign RolloverTemplates to them dymanically in code behind.
I add the series into sciChartSurface.RenderableSeries.
All this works.

When user clicks a series, a selectionChanged eventHandler method tries to switch the RolloverMarkerTemplate of the selected series

ControlTemplate ylbl = (ControlTemplate)Application.Current.Resources["RolloverLabelTopTemplate"];
 flrseries.RolloverMarkerTemplate = ylbl;

The template object is created from Resources and assigned to the series, but the visible presentation is not changed.

Is there a better ( = working) way to do this or is it even possible ?